The present invention relates to a technique for testing a magnetic tape drive, and more particularly, it relates to a technique for improving order of movement of a magnetic head to access all wraps in a read/write test on the magnetic tape drive so as to reduce test time.
A magnetic tape drive is subjected to a read/write test, in which predetermined data is written to a magnetic tape upon completion of assembly or on occurrence of a fault during actual operation and the written data is then read to check performance. The magnetic tape has a plurality of data tracks defined as a recording area across it corresponding to a plurality of conversion elements of a magnetic head, which is called a wrap. In the read/write test, for all the wraps, test data (hereafter, referred to as a test pattern) is written on a test length portion equivalent to five percent or so of overall tape length while switching a magnetic head position and the written test pattern is further read.
This read/write test has an object of reading and writing a test pattern for all the wraps and verifying the read test pattern so as to check a function of reading and writing by correctly moving the magnetic head to all the wraps. In addition, it has an object of, on occurrence of trouble in the magnetic tape drive, limiting existence of a cause of the trouble such as whether the tape or the drive has a problem. For instance, in the case where trouble occurs in actual operation or normal operation and good results are acquired by conducting the read/write test on a different tape from the one used for the operation, it can be presumed that the tape used on occurrence of the trouble has a problem. Moreover, in the case where it passes the read/write test, it can be presumed that the tape has no problem and the drive has the cause.
Conventional magnetic tapes are relatively short in overall length and low in bit density, which means the number of wraps is small, so that a problem seldom occurs even if 5-percent test length is adopted. Therefore, the read/write test on each individual wrap has been conducted in order of moving the head in a normal operation of the drive, that is, according to a wrap sequence in the normal operation. A contributing factor to this is that it is easier to use a program of the wrap sequence to be used in the normal operation rather than to create a special sequence program for the test. However, while the conventional tapes have 30 GB or so of storage capacity, recent tapes are as long as 600 meters with the number of wraps twice as many as conventional tapes and increased storage capacity of 100 GB so that the read/write test conducted in the conventional wrap sequence requires test time of as long as 40 minutes.
Reduction of the test time is strongly required to address the trouble occurring in manufacturing processes of magnetic tape drives and in their active state, and attempts to implement it have been made so far, without sufficient results, by reducing the test length of the tapes by up to 0.5 percent of the overall test length or improving servo control systems.
The inventor noted when shortening the test length of the tapes that, as a factor responsible for the test time, the time required for the magnetic head to move among the wraps is important, which was not noteworthy when the test length of the tapes was long. It was also noted that, to achieve the object of the read/write test, the wrap sequence does not have to be the one in the normal operation as far as all the wraps can be read and written. Thus, an object of the present invention is to provide a method for conducting the read/write test on the magnetic tape drive in a short time. Another object of the present invention is to provide a magnetic tape drive capable of conducting the read/write test in a short time.
A principle of the present invention is to utilize the fact that time when switching a magnetic head from one wrap to another wrap is different depending on mutual physical relationship between the wraps before and after the switching in a read/write test on a magnetic tape drive so as to select order of switching wraps, namely, a wrap sequence that is optimum. Another principle is to select a wrap sequence suited to the read/write test by paying attention to a characteristic that changing to a write mode after a read mode requires time to write to a buffer.
An aspect of the present invention is to make the wrap sequence different from the one in a normal operation of the drive. While the order of switching wraps in the read/write test has been that in the normal operation conventionally, this order has been prescribed in specifications due to other elements such as data recording performance of the tape, not considering time for the read/write test.
While the time for switching wraps is not a problem as time for reading and writing in the actual active state of the magnetic tape drive since it moves on to a next wrap after writing in overall length of the tape for a certain wrap, it is significant to adopt the wrap sequence different from the one in the actual active state in the read/write test since the wrap sequence influences test time greatly because of short test length.
In another aspect of the present invention, order of data bands to be accessed by the magnetic head is set up first. Next, test patterns are consecutively written to all the wraps included in either a forward wrap group or a backward wrap group for each of the data bands selected in the set up order. As for the selected data bands, while it may move on to another data band after writing only to all the wraps included in the forward wrap group, or it may move on to another data band after writing only to all the wraps included in the backward wrap group, or, it may further write to all the wraps included in the forward wrap group and subsequently to all the wraps in the backward wrap group of the same data band, it consecutively writes to all the wraps included in either one of the wrap groups. Consecutively means that, while writing to the wrap group in a certain direction, the magnetic head does not move to another wrap group when it moves from one wrap to another wrap. However, order of writing to the wraps included in a certain wrap group can be arbitrarily selected.
Next, test patterns are read as to the wrap groups written according to the set up order of the data bands. Reading is also performed consecutively in a unit of the wrap group on the wraps included therein so as not to move to another wrap group while reading. It becomes unnecessary to change movement direction of the tape when switching wraps within the same band by writing or reading in the unit of wrap group in a certain direction, and the time for switching wraps can be reduced since it is conducted within the same data band. The read test patterns are verified by software or hardware. To be more specific, it is determined by whether the written test patterns are correctly read. It is possible to prepare a filter by hardware equivalent to the test patterns to verify whether the read test patterns can pass through it, or to compare the written test patterns to the read test patterns.
In a further aspect of the present invention, writing according to the above aspect is performed on all the wrap groups including the forward and backward groups and then reading is performed therefrom. As it takes extra time to write to a buffer if the modes of reading and writing the wrap groups are changed, writing is performed first on all the wrap groups, that is, all the wraps included in all the data bands and then reading is performed therefrom so that it is sufficient to write the test patterns to the buffer just once.
A still further aspect of the present invention relates to a magnetic tape drive having the above forms. A program recording a wrap sequence for testing is stored in a recorder such as a ROM as a program that is different from a wrap sequence in the normal operation, and is executed by a central processing unit (CPU) on the read/write test.
FIG. 1 is a diagram schematically showing configuration of a magnetic tape;
FIG. 2 is a diagram schematically showing configuration of wraps on data bands;
FIG. 3 is a diagram schematically showing configuration of a magnetic head 201 applied to an embodiment of the present invention;
FIG. 4 a diagram showing partial details of the wraps;
FIG. 5 is a partial block diagram of the magnetic tape drive described as the embodiment of the present invention;
FIG. 6 is a flowchart showing the basic procedure of the read/write test;
FIG. 7 is a diagram showing relationship between the time required for movement of the head for switching the wraps and switching patterns;
FIG. 8 is a diagram showing wrap groups of the magnetic tape used in the embodiment of the present invention;
FIG. 9 is a diagram showing the wrap group sequence wherein a total of time for switching wrap groups and time for writing to a buffer is the smallest; and
FIG. 10 is a diagram showing the wrap sequences created based on selected wrap group sequences.